Amphibians: Characteristics, Evolution, and Diversity - A Science Lesson

Section 3: Amphibians Most amphibians begin life as aquatic organisms and then live on land as adults. K W L What I Know What I Want to Find Out What I Learned Essential Questions What were the kinds of adaptations that we...

Section 3: Amphibians Most amphibians begin life as aquatic organisms and then live on land as adults. K W L What I Know What I Want to Find Out What I Learned Essential Questions What were the kinds of adaptations that were important as animals moved to the land? What are the characteristics of amphibians? What are the differences between the orders of amphibians? Copyright © McGraw-Hill Education Amphibians Vocabulary Review New metamorphosis cloaca nictitating membrane tympanic membrane ectotherm Copyright © McGraw-Hill Education Amphibians Evolution of Tetrapods The move to land Tetrapods are four-legged vertebrates that first appeared on Earth 360 million years ago. Several physical challenges in the move from water to land Copyright © McGraw-Hill Education Amphibians  Evolution of Tetrapods How did vertebrates adapt to life on lands? Conditions are much different on land than in water. The table below compares conditions in water and on land. It also lists some important adaptations that enabled vertebrates to live on land. Copyright © McGraw-Hill Education Amphibians  Evolution of Tetrapods What land habitats do animals occupy? Land provides many habitats for animals. With proper adaptations, animals can occupy tropical rain forests, temperate forests, grasslands, deserts, taiga, and tundra. Copyright © McGraw-Hill Education Amphibians Characteristics of Amphibians Most amphibians begin life as aquatic organisms. After undergoing metamorphosis, they are equipped to live on land. A frog begins life as a limbless, gill- breathing tadpole. The tadpole undergoes metamorphosis daily. Hind legs form and grow longer, and forelimbs sprout. The tail shortens. Lungs replace gills. Soon the tadpole becomes an adult frog. Copyright © McGraw-Hill Education Amphibians Characteristics of Amphibians Most amphibians have four legs, moist skin with no scales, a double- loop circulatory system, and aquatic larvae. They exchange gases through both their skin and lungs. Copyright © McGraw-Hill Education Amphibians Characteristics of Amphibians How do amphibians feed and digest? Most frog larvae are herbivores, whereas salamander larvae are carnivores. As adults, their diets are similar as both groups become predators. They feed on a variety of invertebrates and small vertebrates. Some salamanders and legless amphibians catch prey in their jaws. Frogs flick out their long, sticky tongues to catch flying prey. Copyright © McGraw-Hill Education Amphibians  Characteristics of Amphibians How do amphibians feed and digest? Food moves from the mouth through the esophagus to the stomach, where digestion begins. The food moves to the small intestine, which receives enzymes from the pancreas to digest food. From the intestine, food is also absorbed into the bloodstream. From the small intestine, food moves to the large intestine before waste is eliminated. The intestines end in a chamber called the cloaca, which receives wastes and reproductive cells before they leave the body. Copyright © McGraw-Hill Education Amphibians  Characteristics of Amphibians How are wastes removed from the body? The kidneys filter wastes from the blood. Amphibians that live in water excrete waste as ammonia. Amphibians that live on land excrete urea. Urea is made from ammonia in the liver. Unlike ammonia, urea is stored in the urinary bladder until it leaves the body through the cloaca. Copyright © McGraw-Hill Education Amphibians Characteristics of Amphibians What structures are used for gas exchange? As larvae, most amphibians exchange gases through their skin and gills. As adults, most breathe through lungs, their thin, moist skin, and cavities in the mouth. Copyright © McGraw-Hill Education Amphibians Characteristics of Amphibians How does blood circulate through the body? Amphibians have a double-loop circulatory system. In the first loop, oxygen-poor blood moves from the heart to pick up oxygen in the lungs and skin. Oxygen-filled blood then moves back to the heart. Copyright © McGraw-Hill Education Amphibians Characteristics of Amphibians How does blood circulate through the body? In the second loop, oxygen-filled blood moves from the heart through vessels to the body, where oxygen diffuses into cells. The amphibian heart has three chambers. The right atrium receives oxygen-poor blood from the body. The left atrium receives oxygen-filled blood from the lungs. The ventricle remains undivided. Copyright © McGraw-Hill Education Amphibians Characteristics of Amphibians How have the brain and senses adapted? Amphibians use sight to locate and capture prey that fly at high speeds and to escape predators. Frogs have nictitating membranes, clear eyelids that protect the eye. Frogs use their tympanic membrane, or eardrum, to hear high- pitched sounds and to amplify sounds from the vocal cords. Copyright © McGraw-Hill Education Amphibians Characteristics of Amphibians How do amphibians control body temperature? Amphibians are ectotherms that obtain their body heat from the external environment. Copyright © McGraw-Hill Education Amphibians Characteristics of Amphibians How do amphibians reproduce and develop? In most amphibians, fertilization is external and the shell-less eggs must be laid and fertilized in water. Tadpoles hatch from the egg and undergo metamorphosis from a fishlike animal to an air-breathing one. Copyright © McGraw-Hill Education Amphibians Amphibian Diversity Scientists classify modern amphibians into three orders. Order Anura includes frogs and toads. Order Caudata includes salamanders and newts. Order Gymnophiona includes caecilians. Copyright © McGraw-Hill Education Amphibians Amphibian Diversity What features distinguish frogs from toads? Frogs have longer and more powerful legs and can make more powerful jumps than toads. Frogs have moist, smooth skin, while toads have bumpy, dry skin. Both need to be near water for reproduction. However, toads generally live farther from water than do frogs. Unlike frogs, toads have glands near the back of their heads. These glands release a foul-tasting poison to discourage predators from eating them. Copyright © McGraw-Hill Education Amphibians  Amphibian Diversity What are features of salamanders and newts? Salamanders and newts have long, slim bodies with necks and tails. Most salamanders have four legs; thin, moist skin; and lay their eggs in water. Their larvae look like small salamanders with gills. Salamanders must live near water. They live in moist areas, such as under logs or in leaf litter. They feed on worms, frog eggs, and insects. Newts are aquatic throughout their lives. Copyright © McGraw-Hill Education Amphibians  Amphibian Diversity How do caecilians differ from other amphibians? Unlike other amphibians, caecilians have no legs. They are wormlike. They burrow in the soil and feed on worms. Skin covers their eyes, so they might be nearly blind. They have internal fertilization and lay their eggs in moist soil near water. Caecilians live in tropical forests. Copyright © McGraw-Hill Education Amphibians Review Essential Questions What were the kinds of adaptations that were important as animals moved to the land? What are the characteristics of amphibians? What are the differences between the orders of amphibians? Vocabulary cloaca tympanic nictitating membrane membrane ectotherm Copyright © McGraw-Hill Education Amphibians